8 3/4 pinion seal

Hello everyone - I hope someone can help.
Last year I replaced the pinion seal on my 1968 Road Runner 8 3/4 "742" case. After receiving a new seal and then comparing it to an NOS seal, I went with NOS since it was obviously more beefy and the newer one appeared cheap and thin (both the rubber and the metal).
Here I am a year or so later, and the seal is leaking again. Not sure if it was faulty or whether I didn't tork the pinion nut tight enough.
I used a tork wrench and it did not leak until now....
Anyone have any good tips? I plan on installing another NOS seal this weekend. Oh, I do not have a lift. I jacked up the car and used jack stands - which also makes tightening/loosening with a breaker bar a biotch - not much leverage.

How old are the NOS seals? Rubber does have a shelf life.

Not sure on the actual age of the seal, but the rubber portion is plyable and doesn't appear brittle.
The new seal I purchased last year (and returned) just seemed like junk.

When you had the yoke off did you check it fir a noticable groove warn into it from the old seal?

No, I didn't check, but to give some history, I purchased this 742 chunk from Mancini's back in 1997. It was rebuilt with new gears, etc. I put MAYBE 1500 miles on this care since I replaced the center section.

C'mon people, please help me out.

I would check that yoke to see if it has a groove.
Did you get the front of the housing clean and use silicone?

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I would check that yoke to see if it has a groove.
Did you get the front of the housing clean and use silicone?

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You need to look at the yoke for a groove where the seal rides , and does it have a DUST SHEILD?? There was a REASON the factory installed dust shields on yokes and for some reason the aftermarket deemed them NOT NECESSARY . Also are you sure it's leaking from the SEAL and not getting past the splines and leaking from under the yoke nut/washer?

I agree on the NOS seal thing , rubber does not last forever and I'm pretty sure the original seals on 742's were LEATHER , contact Dr. Diff he has a GOOD 742 seal available .